By "cap" I mean set a maximum level of hit points a character can acquire, let's say 20 hit points.

I realize D&D is intended to be heroic fantasy, and there are other RPG systems which are more realistic than D&D about hit points, combat injuries, etc.

But for argument's sake, if I want to stick with D&D but limit hit points, is it a simple tweak I can make as a DM or will I have to make adjustments throughout the rules and not be worth the effort?

My goal is to make the game a bit more realistic. In my opinion, the suspension of disbelief and tension that make low-level D&D fun starts to evaporate when players become nearly invincible and can take on armies & dragons single-handedly, blow off law enforcement, fall from great heights w/out dying, etc. all because they can absorb an inhuman amount of punishment. For example, I’d like high level fighters to resemble Aragorn from LOTR, who can square off against a dozen Orcs relying on his superior swordsmanship, rather than the godlike Thor who barely works up a sweat smiting frost giants.

Edit: As a corollary - should characters be compensated in other ways as they advance levels to maintain balance for high level game play?

Will you also be capping damage? If not, you'll run into the issue (at higher levels) of attacks or spells that will instantly kill without/despite a save.
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DakeyrasDec 11 '13 at 17:28

No, but good point. High level foes will be quite deadly.
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RobertFDec 11 '13 at 17:37

7

Doesn't apply to all editions in the same way: in earlier D&D, your HD is already capped, and you only get +1 or +2 hp per level after. (Nevermind that level also capped around 10 for some PCs, and monster HD and damage output was far, far lower.)
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SevenSidedDieDec 11 '13 at 17:38

What exactly are you trying to accomplish with this change? A number of alternatives to the 3.5 HP system have been devised, and most of them involve smaller numbers, not unlike your idea of a cap, but they're best suited to different styles of play. Knowing exactly what issue you're trying to solve will help us find the best match for your particular issue.
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The SpooniestDec 11 '13 at 20:13

8 Answers
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This is an extremely arbitrary change that will break a lot of the intended functioning of the system

The system is designed with certain HP values in mind. Damage scales rapidly with level, in fact faster than HP does, and thus after only a few levels past the cap, just about everything will kill in one shot.

The system was already broken though.

Enough optimization, and most melee types can one-shot just about anything of a remotely appropriate level that they can get their hands on. This just makes doing that much (much) easier.

Ultimately... perhaps it would “work.”

But most players don’t play at those optimization levels, and most combats are not supposed to be decided by initiative, even if at the highest optimization level that’s often what it comes down to. Gentlemen’s agreements, ban lists, houserules, usually they’re designed to mitigate if not eliminate the rocket-tag nature of D&D, while this would put it into overdrive.

It would be very strange, and extremely lethal. Death would be common, and would frequently be arbitrary. Characters will often die without actually getting a turn in which to do anything to try to prevent their death. Ambushes would be almost impossible to survive; a single rogue archer getting a full-attack before anyone else has gone (i.e. they’re flat-footed), or from a hidden location, could easily kill the entire party in one turn. Initiative would be, by far, the most important combat stat (which it arguably already was), because whoever goes first, will kill the enemy before that enemy can go, most of the time.

Which doesn’t sound like an overly fun game to me, but I gather some do prefer it. As I said, at high enough optimization levels you can force the game into that mold anyway. At least this change eliminates the “skill gate” for you to get in on the super-lethal combat.

If that’s what you want, and more importantly, if you can find players who want that, maybe it could “work,” for a given definition of working. I wouldn’t play, I don’t think I know anyone who would be interested in playing it, but maybe you can find them.

But you perhaps misunderstand HP

Based on this comment:

But there are other solutions - give PCs so many free rerolls (favors from the Gods...) for each adventure (or per level), something used in Deciphers's LOTR RPG. Or be generous with magic armor & shields. Magic armor is a good proxy for extra hit points, minus all the hand-waving trying to explain how a PC can survive unbelievable amounts of damage.

I think you are misunderstanding the breadth of HP’s abstraction: it does not (necessarily) represent physical health, nor does lack of it (necessarily) represent injuries and wounds.

It also represents favors from gods, innate magic, destiny, luck, morale, and so on. Damage can be done from a lot of causes, and it can also be healed in a lot of ways (there are healing effects that derive their effect from inspiration, for instance, and some of those are extraordinary, i.e. nonmagical, in nature). HP is a large and expansive abstraction, but it’s not just “characters can soak absurd numbers of wounds and injuries.” It’s often closer to “plot armor.” Note also that loss of HP does not result in penalties due to wounding. Part of that is simplification and cinema, but part of it is also an acknowledgement of what HP is not, namely wounds and injuries.

Vastly superior option

As everyone has been saying, E6 is the way to go. E6 allows you to maintain that “low-level” feel, capping players at 6 class levels (and that includes 6th-level HP), but allows them to continue to gain XP, which they can trade in for bonus feats. It’s a great system, giving just enough to keep the game moving and the characters growing, while preventing more powerful effects that greatly change the nature of the game from getting into play.

Yeah, this is totally feasible in D&D 3.5e. Most of the work to identify and mitigate impact on other rules has already been done for you even, since this is the kind of powered-down D&D that E6: The Game Inside D&D* implements.

You could just play E6, which (for those who aren't familiar and haven't read the link yet) is D&D with a level cap at 6, plus a handful of extra rules and guidance for how to handle monsters and how "advancement" works after you hit the level cap. E6 has been played a lot too, so it's been stress-tested successfully around the world.

Or, you could stick with your HP-cap houserule and just take a look at the encounter-prep guidance in E6 to use as a guide to DMing lower-powered D&D heroes – especially how to use monsters, and which.

Basically, the work's be largely done for you already – it's just a matter of tweaking it to your taste now. Since your questions is largely whether it's feasible (and less how), the existence of E6 pretty much answers the "whether" with a resounding "yes". Tweak to your heart's content, pay attention to unexpected side-effects, and continue making adjustments until the play experience is stable and plays the way you like.

For other editions, this is feasible too. Trickier in 4e, I imagine, because that's more of an interlocking system, but in earlier D&Ds it would be pretty trivial a change, since the HP totals and damage output are already much lower in those editions. Like in E6, simply don't use monsters that are more powerful than the heroes, unless they're supposed to be near-impossible, legendary foes. I might scale the HP cap depending on class (say, 3× the hit die size?) to give fighty classes a bit of a boost over non-fighty classes, but even then I might not bother.

+1, E6 is definitely the first place to look in considering this. It works wonderfully and even if you chose not to use E6 it can point you toward how to make your own customizations.
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Jeff FryDec 11 '13 at 19:03

As it stands, this is a bad idea. All you will do is very quickly make a 'shoot first to win' scenario out of every battle. A single attack will be often be lethal even if the victim makes the save.

Problems

A fireball of 6d6 averages 21 damage, assuming the caster hasn't raised his damage in other ways (not that they'd need to, in most cases). This means that any 6th-level wizard or sorcerer can AoE insta-kill most creatures - including player characters!

Also, meat-shields would no longer be effective, weakening tank classes, along with healing spells, and casters - especially those who can summon creatures - would become even more powerful.

Houserules to balance the game again

The only ways that spring to mind to balance this would be to hand out DR like candy, and/or have such high saves and armour class that the characters are untouchable - but a natural 20 will still kill in these cases. Overall, there's no good way to nerf character HP without also cutting down damage or expecting your players to resurrect or re-roll several times a session.

Best alternative

E6 (another link) seems like it'd work quite well. It stops your players from leveling past level 6, which would automatically limit their hit points. Instead, they get feats every 5000xp. This looks like it could replace the limits on player health, and then limiting monster health isn't as broken either since the player characters can't consistently cause, say, 30 damage (if you set the cap at 30 or higher, this would be a quite elegant solution).

Other alternatives

An alternative solution could be to replace HP with a more lethal system instead, or increase potential damage. Making all damage dice explode makes a dagger blow much more threatening, since you could roll several 4's in a row quite easily over the course of a long game. The stress tracks from FATE might also be more suitable, if you can find a good way to port them over. Lastly, consider switching to a system that places more emphasis on danger, such as Harnmaster (known for being both dangerous and simulationist).

tl;dr

You can't cap hit points in D&D 3.5 without seriously breaking the game, and there aren't really any ways to completely fix the problems you cause. Instead, look at capping monster hp and using the E6 system for the players.

This will create a lot of problems for you! As enemies level up, their damage output increases. If you try to cap damage also, there is less to separate a big threat from a weak enemy.

Eventually, this cap on hp will be reached by all players, which will mean that there is no advantage in terms of hit points for one class over another. This would be great for a wizard, but really suck for a barbarian.

You would also make feats like 'Toughness' become useless at higher levels.

I think this is more than just a lot of effort,but rather I think it is unfeasible altogether.

Note that "less to separate a big threat from a weak enemy" can be a desirable feature! Less need to mess with monster advancement rules, and more opportunity to use the vast range of monsters at every PC level.
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SevenSidedDieDec 11 '13 at 17:41

This rewards classes that don't gain as many HP. If my fighter hits HP cap at level 3 and my wizard catches up by level 6, what did my fighter gain by having d10s for HP instead of d4s?

You could have a different limit per class. But that gets weird in the case of multiclassing. You could also treat max HP as a property earned by first level (similar to how you roll max on your first level's HP die roll and get 4x skill points), but I haven't really thought that through.

HP dice aside, this also punishes constitution as a stat. I think I'm okay with that though, because it's a pretty popular stat. The dwarven race won't be happy.

In addition to the E6 suggestion others have made, you may want to look at some of the OSR D&D clones - many of them either directly use the older edition caps of Hit Dice or similar.

Also, if your goal is to make things more gritty, there's a couple of other options you can also use that keep the basic system of hitpoints, but prevent folks from simply wandering through deadly damage like it was a light mist:

The System Shock Rule

An old rule was the 50 hitpoint system shock roll. If a character took 50 hitpoints from a single source of damage, they'd have to make a system shock roll (a specialized form of saving throw, basically) or die on the spot.

The nice thing is that you can scale that number up and down to what fits, though realize that also incentivizes the players to look for doing that kind of damage to other folks as well - if you say, "10 hp is the limit" everyone's going to be looking for those two handed weapons, etc.

Hitpoints vs. Lifepoints

Some rpgs do something where they basically have 2 sets of hitpoints, one of which is the "bruises and endurance" sort of hitpoints, the other which is the life threatening "Oh god I punctured my lung" sort of hitpoints. The super important type of hitpoints are usually capped or at least grow so slowly they might as well be.

What this does is it allows for folks to generally get tougher BUT still potentially go down from a lucky strike. You can do stuff like:

Critical hits go straight to Life Points

Damage above a certain number in a single hit goes to Life Points

Certain types of attacks/damage go straight to Life Points

Rolling X above the required to hit number goes straight to Life Points

Damage is split - a certain amount goes to less threatening Hit Points, a certain amount to important Life Points, etc.

Be aware, of course, that this also means players will be looking to DO just that thing and check whatever version of D&D you're using doesn't make that trivially easy or accessible to only a few classes. ("What's that? Negative Energy goes straight to murder points? Well, hello Chill Touch")

It achieves the basic goal of low HP numbers that you seem to be after here: everyone has a 25-point "life bar," and there is no way to extend it. Instead, you have to use other means to become tougher as level rises, such as dodge bonuses and DR (including a universal form of DR which they call "Soak"). Tactical movement and defense, especially concerning things like cover, become much more important, and monsters become terrifying.

This shouldn't cause much of a problem in 3.x, so long as we're not talking very drastic caps (such as capping at 15hp) and, of course, you are taking it into consideration when developing your scenarios.

In your particular case, what you might do instead of putting in a fixed cap is reduce hit dice at higher levels. As an example, levels 1-5 use their regular dice HP, levels 6-10 use the next die down (d10 -> d8), the next 5 levels use 2 steps down, etc. This way you are gradually winding down the HP escalation, without arbitrary and drastic caps.